The present invention relates generally to improving surface smoothness, surface hardness, and compatibilizing polyolefin or polyolefin composite materials to functional polymers. A method of producing such materials from a polyolefin/polyolefin composite substrate that is topologically/mechanically bonded to a reinforcing mat formed from reinforcing fibers and thermoplastic polymer powder is described.
Plastic sheet materials made from polyolefin or polyolefin composite materials are widely used in the manufacture of molded articles. Such materials suffer from bonding issues, little to no surface abrasion resistance, coupled with composite form process issues. Accordingly, when used for certain applications such as, for example, high impact paneling, woven fiberglass/polyolefin materials have a tendency to develop sink marks that many consumers find detrimental to their aesthetic appearance. It should also be appreciated that polyolefin and polyolefin composite materials are often difficult to adhere or bond to other materials. This can limit the application of these materials particularly where decorative attributes are required.
A need is therefore identified for a way to effectively provide surface enhancements and improved bondability to polyolefin and polyolefin composite materials. Preferably, the fiber reinforcement will be accomplished in a manner that not only provides increased strength and rigidity when employed with straight polyolefin materials but also compatibilizes the polyolefin and polyolefin composite materials for better bonding to other materials and also functions to provide smoother surfacing and a wider range of decorative possibilities. The present invention successfully achieves these goals while also minimizing the application of heat to the polyolefin/polyolefin composite material prior to molding into the final product shape. Thus, a number of important properties including surface energy, surface smoothness, and improvements in impact, flexural and tensile strengths of straight polyolefin materials can be achieved.
In accordance with the purposes of the present invention as described herein, a compatibilized polyolefin/polyolefin composite material is provided. That material comprises a polyolefin/polyolefin composite substrate and a reinforcing mat. Bonding between chemically incompatible groups within the mat and polyolefin is achieved through a mechanical bonding or topological affect whereby the polyolefin material flows into the reinforcing mat layer, gets caught between the more viscous mat binder, and achieves a mechanical interlock.
The reinforcing mat is formed from reinforcing fibers selected from a group consisting of glass fibers, carbon fibers, aramid fibers, kenaf fibers, hemp fibers, cellulose fibers and mixtures thereof and a thermoplastic polymer powder selected from a group of materials consisting of phenolic powders, phenoxy powders, polyester melt adhesive powders, modified polyethylene powders, PVC/PVDC copolymer powders, EVA powders, PVA powders, acrylic powders, polyester powders, PVC/PVAc copolymer powders and mixtures thereof.
The phenolic powders include novalak, cresol type and resorcinol type powders. More specifically describing the invention, the phenoxy based epoxy powders include various melting point materials made possible by increasing the degree of polymerization between Bisphenol A and epichlorohydrin. Polyester melt adhesive powders include low molecular acids, such as terephthalic, adipic, isophthalic, phthalic, azelaic, linoleic, oleic and sebacic, reacted with diols such as ethylene glycol, 1,4 butanediol, 1,6-hexanediol and 1,4-cyclohexanedimethanol. In all cases, the melting point of the mat binder should either exceed the melting point of the polyolefin or the selected binder must be considerably more viscous than the selected polyolefin.
The modified polyethylene based resin powders include acid modified and/or maleic anhydride grafted polyolefins combined with a filler to increase the specific gravity of the powder to at least 1 gm/cm3. The polyester powders include thermosetting type polyesters that employ multifunctional acids and diols. The acrylic powders include higher glass transition acrylics like polymers formed from methacrylic acid, acrylic acid and methyl methacrylate or thermosetting acrylic materials that employ functional hydroxy groups like 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and the like.
The reinforcing fibers provided in the mat have a diameter of between about 10 to about 23 microns and a length of between about 0.25 to 1.5 inch. The reinforcing fibers are provided in the reinforcing mat at between about 20 to 40 weight percent and the thermoplastic polymer powder is provided at between about 60 to 80 weight percent. In accordance with an additional aspect of the present invention the mat may also incorporate an emulsion polymer binder. That emulsion polymer binder may be an acrylic emulsion. Where the mat incorporates an emulsion polymer binder, the reinforcing fibers are provided at between about 20 to 40 weight percent, the thermoplastic polymer powder is provided at between about 40 to 75 weight percent and the polymer binder is provided at between about 5 to 10 weight percent. The purpose of the emulsion binder is to minimize possible fiber dusting complaints during the final consolidation step by providing further bonding ease of the thermoplastic powder to the reinforcing glass fibers.
In accordance with still another aspect of the present invention, the compatibilized polyolefin/polyolefin composite material may further include a film against the mat so that the mat is disposed between the film and the polyolefin/polyolefin composite substrate. The film is formed from a material selected from a group consisting of PVC, PVC/PVAc copolymer, PVC/PVDC copolymer, PVDC, ABS, acrylic, polyester and mixtures thereof.
In accordance with an additional aspect of the present invention, a method of compatibilizing a polyolefin/polyolefin composite material is provided. The method includes contacting a reinforcing mat formed from reinforcing fibers selected from a group consisting of glass fibers, carbon fibers, aramid fibers, kenaf fibers, hemp fibers, cellulose fibers and mixtures thereof and a thermoplastic polymer selected from a group of materials consisting of phenolic powders, phenoxy based epoxy powders, polyester melt adhesive powders, modified polyethylene based resin powders, PVC/PVDC copolymer powders, EVA powders, PVA powders, acrylic powders, polyester powders, PVC/PVAc copolymer powders and mixtures thereof with a polyolefin/polyolefin composite substrate. Still further, the method may include a polymer binder in the mat such as an acrylic emulsion. Additionally, the method includes a step of applying sufficient temperature and pressure for a sufficient time to consolidate the mat and substrate.
More specifically describing the invention, the method includes selecting a pressure of between about 50 to about 300 psi for application to the mat and substrate at a temperature between about 350 to about 450EF for a period of time of between about 10 to about 300 seconds.
In addition, the method may include the step of adding a film against the mat. The film is selected from a group of materials consisting of PVC, PVC/IPVAc copolymer, PVC/PVDC copolymer, PVDC, ABS, acrylic, polyester and mixtures thereof. Films are normally applied for various purposes including decorative, UV resistance, or enhanced bondability to decals.
Advantageously, the resulting compatibilized polyolefin/polyolefin composite material is only subjected to one heat treatment to both (a) consolidate the mat and substrate together and (b) mold the material into its final shape. Since this is done in a single heating step, the material is subjected to fewer heat cycles and the material accordingly has observed less thermal cycles. It is also provided with veil possibilities and the polyolefin/polyolefin composite material is made more compatible for binding with other materials. When employing woven glass/polyolefin composites, sink marks often occur without the presence of a surfacing veil. This invention provides surfacing veil characteristics coupled with enhanced surface bondability in a single step. Although alternative methods of bonding polyolefin materials to other materials exist, as is made possible by grafting acrylic acid, maleic anhydride, and other function groups, and/or by the incorporation of corona discharge, plasma treatment, or flame treatment, these alternative methods can not provide smoothening effects, a harder more scratch resistant surface, or permanent chemical changes without grafting reactions.
In the following description there is shown and described the preferred embodiment of this invention simply by way of illustration of several modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.